Positive photoresists for use in semiconductor structure production processes should simultaneously have properties such as the property of becoming alkali-soluble in an irradiated portion upon light irradiation; adhesion to a silicon wafer; and plasma etch resistance. The positive photoresists each generally include a polymer as a base resin, a photoacid generator, and some kinds of additives to adjust the properties.
With finer design rules of semiconductor integrated circuits, exposing sources with shorter and shorter wavelengths have been used in lithography for semiconductor production. The exposing sources are now moving from KrF excimer laser at a wavelength of 248 nm to ArF excimer laser at a wavelength of 193 nm. Resist polymers for use in KrF or ArF excimer laser exposure include monomer units that release a moiety thereof by the action of an acid generated from a photoacid generator and exhibit solubility in an alkaline developer. Some of known monomer units of this type contain an acid-leaving group including a large alicyclic structure and are exemplified by a monomer unit derived from 2-methyl-2-methacryloyloxyadamantane, and a monomer unit derived from 1-(1-methacryloyloxy-1-methylethyl)adamantane (Patent Literature (PTL) 1, PTL 2, and PTL 3). Resins for photoresists containing any of these monomer units are, however, insufficient in resolution, pattern shape, and/or developability.
In contrast, others of the specific monomer units contain an acid-leaving group including a small alicyclic structure and are exemplified by a monomer unit derived from 1-(1-methacryloyloxyethyl)cyclopropane (PTL 4). Resins for photoresist including the monomer unit are, however, insufficient in sensitivity.